This project deals with the immunobiology of HLA and its clinical applications. Studies will focus on three areas. One is to identify and characterize B cell specific alloantisera, to evaluate linkage of B cell alloantigenic determinants to HLA, and to characterize the role of such antigens in lymphocyte activation in the mixed leukocyte culture and in the secondary allogeneic response. We also will search for HLA-D homozygous typing cells with new specificities and study possible subdivisions of HLA-D specificities and determine the relationship between HLA-D and PLT determinants. Studies of HLA and disease associations will concentrate on juvenile diabetes mellitus, especially in American Blacks, thyroid neoplasia and acute lymphocytic leukemia.